Taking the world by storm is this seemingly simple logic-based number puzzle known as Sudoku. At first blush, the partially filled puzzle on a 9x9 grid looks rather easy to solve, but like crosswords, its levels can range from easy to hair-pulling hard, depending on how the sokdu puzzle setter maps it out.
The grid is made up of 9 rows and 9 columns, for a total of 81 squares. It’s solved by filling the squares in with numbers from 1 to 9 by using each number just once for every column and every row. In addition, there are nine 3x3 sub-squares within which each of the numbers 1 to 9 should likewise be used only once.
Number puzzles similar in nature have been around as early as the 19th century, but the Sudoku we know now was introduced in Japan in 1986 via the puzzle and games publication known as Nikoli. “Sudoku” actually means “single number.” At around 2005, Sudoku’s popularity started to spread worldwide.
Erroneously thought to be a Japanese invention, it was believed to be the brainchild of an American named Howard Garns, a puzzle setter for Dell Magazine. Dell published the earliest forms of the modern Sudoku in 1979. It was then called “Number Place.”
It is said that you need to perform three processes in order to solve this puzzle: scan, mark up, and analyze.
The process of scanning involves two techniques: cross-hatching and counting 1-9 in different areas. The former refers to the method of checking the rows to pinpoint which particular square on a line may possibly hold a certain number using the process of elimination. The columns are checked in the same manner.
The Sudoku solver scans when starting to solve the puzzle, and regularly – once between analyses – while solving. Scanning must be done systematically, not randomly, so you won’t miss any areas. Don’t forget to scan in reverse. This means checking for places where a number cannot possibly be written in.
Counting 1-9 in various parts of the puzzle – its rows, columns, and regions – can also make filling in quicker. Once you’re done searching for possible squares for number 1, for instance, move on to 2, and then to 3, etc.
If you’re a beginner, you would need a certain system of “taking down notes” in order to remind you of the possible numbers for a square.
One easy method is to use the dot notation. Imagine each square as the facet of a die, consisting of 9 dots in 3x3 fashion. Assume that the first-row dots are the numbers 1-3, those on the 2nd row represent 4-6, and those on the bottom row mean 7-9. If you’re certain that a square can possibly hold either a 2 or a 9 only, you can then mark the square with a dot on its upper middle part (to represent 2) and another at its bottom right part (to mean 9).
The process of analyzing also has two approaches – the candidate elimination approach and the ‘what-if’ technique. The former refers to the method of eliminating candidate numerals, one after another, to come up with just one certain choice. After every final answer, another scan is performed just to see if any progress has been made, improving the likelihood of filling in more “sure” answers.
The ‘what-if’ technique, on the other hand, involves a square with two possible numbers, and simply put, this id the trial-and-error technique where one of the numbers is tested for duplication. If any duplication is found, then the alternative number must be the correct one.
